Fleece layers are used to lay multiple layers of a card web, produced by a carding machine, as uniformly as possible on an output apron. The card web is usually guided first through an upper carriage and proceeds from there to a laying carriage, through the laying gap of which the card web is deposited onto the output apron. At least two card web conveyor belts are used to guide the card web through the fleece layer. The movements of the card web conveyor belts, of the upper carriage, and of the laying carriage are controlled so as to coordinate with each other.
Fleece layers are often preceded by mechanisms for changing the web line speed. These are used primarily to regulate the density of the card web as a way of profiling the laid fleece or to compensate for increased thickness at the edges of the laid fleece. Mechanisms of this type for changing the line speed include, for example, take-off rolls, driven at different speeds, on the carding machine located upstream of the fleece layer, as known from U.S. Pat. No. 6,195,844, for example, or a separate web drafter, which can be installed between the carding machine and the fleece layer (see, for example, EP 1 532 302 A1).
In both of the patent documents cited above, fluctuations in the line speeds of the incoming web are compensated in the fleece layer by an integrated buffer, which is obtained by increasing the distance traveled by the upper carriage, which results in turn in an increase in the length of the loop in the first card web conveyor belt. For this purpose, a complex control system is required for the upper carriage, so that the buffer loop can be formed and the changes in the speed of the incoming card web can be compensated with precision at every moment of the laying process.